Disposable absorbent articles are well known and all have absorbent elements for absorbing and retaining body fluids; an absorbent element must be able to acquire liquid rapidly and to distribute it internally so as to prevent leakage and must also have a good capacity to retain the fluids when subjected to the normal pressures of use.
Absorbent elements made mainly of hydrophilic fibrous material such as, for example, pads of cellulose fibres, layers of wadding, or the like generally have satisfactory characteristics as regards their liquid-absorption rate and can distribute the liquid effectively within them but are very ineffective from the point of view of retention when subjected to the normal pressures of use.
The use of absorbent gelling materials in combination with hydrophilic fibres in order to increase the absorption and retention capacities of the absorbent elements is known.
Absorbent gelling materials, commonly known as superabsorbents, are polymers which can swell up and absorb large quantities of liquid, particularly water, or also, to a lesser extent, body fluids.
They also have the particular property that they retain the fluids even under moderate pressure; owing to this characteristic, their use in absorbent elements for disposable absorbent articles has been proposed for some time.
With the use of absorbent gelling materials, it is possible to produce absorbent elements which contain less hydrophilic fibres for a given absorption capacity and which consequently have smaller dimensions, particularly thicknesses, than conventional absorbent elements made of fibres alone.
Absorbent gelling materials are commonly incorporated in particle form within fibrous structures. Structures have been formed in which the fibres and the particles of hydrogelling, absorbent material are disposed in separate, generally very thin, superposed layers or, alternatively, the particles can also be mixed with fibres in one of the fibrous layers.
Many particular forms of layered, absorbent structures of this type, in which the fibrous material is represented by one of more layers of wadding, absorbent paper or non-woven fabric, and in which the particles of absorbent gelling material are incorporated in the structure in various ways, are known in the art.
Different types of particulate materials, other than absorbent gelling material particles, can also be incorporated in layered absorbent structures, such as for example odour control materials in particle or powder form.
Usually a continuous, weblike layered absorbent structure is manufactured, which is subsequently cut in smaller pieces to provide the individual layered absorbent structures to be used as absorbent elements in disposable absorbent articles.
Layered absorbent structures incorporating particulate material can be formed directly on the production line for the absorbent articles in which they are to be incorporated, or, alternatively, they can be produced independently as semi-finished products that are sold and stored separately in form of a continuous web-like structure, e.g. wound in a roll, or otherwise held in a container, and are then fed to the production line.
A common problem with layered absorbent structures incorporating particulate material consists in the effective containment of the particles within the structure in a stable manner, e.g. avoiding that the particles move within the structure and become locally concentrated. The particulate material can also escape from the edges of the layered structure, particularly along the edges where the individual structures are cut from the continuous web-like structure, therefore creating a problem both in the production line and in the final product. known solution for the formation of a layered absorbent structure provides for the use of an adhesive, e.g. of the hot melting type, applied to the entire surface of one of the fibrous layers with the dual purpose of bonding the two fibrous layers together and simultaneously fixing the particles of e.g. absorbent gelling material and/or odour control material between them.
The use of an adhesive may, however, affect the characteristics both of the fibrous layer to which the adhesive is applied, and of the particulate material which come into contact with the adhesive.
In general, therefore, it is necessary not to use an excessive quantity of adhesive and consequently the possibility of the loss of particulate material from the edges of the layered structure cannot be completely eliminated.
Different solutions to the problem of the loss of particulate material along the longitudinal edges of a continuous, web-like layered absorbent structure are known, by longitudinal edges being meant the edges of the layered structure that are parallel to the direction of formation of the structure itself.
For example, the continuous, web-like, layered absorbent structure can be completely surrounded with a layer of wadding, or, alternatively, the structure can be provided by means of a single layer of fibrous material on which the adhesive and the particulate material are distributed only on a central longitudinal strip and subsequently the two side portions are folded so that they partially overlap approximately along the longitudinal axis, and are joined e.g. by means of adhesive.
In International Patent Applications WO 94/01069 and WO 95/17868 by Procter & Gamble Company continuous, web-like, thin, layered absorbent structures containing absorbent gelling material for use as absorbent elements in disposable absorbent articles are described. Such layered absorbent structures are formed by at least two fibrous layers comprising between them a layer of particles of absorbent gelling material, the two fibrous layers being joined together by particles of thermoplastic, polymeric, organic material in finely divided solid form distributed and mixed with the absorbent gelling material, and by two lines of adhesive disposed along the longitudinal edges of the structure.
While the above described layered structures do not have the problem of loss of particulate material along the longitudinal edges, they still have a problem of loss or spillage of particles when they are cut transversely relative to the longitudinal direction in the production line in order to form the individual layered absorbent structures that are to be incorporated as absorbent elements in the absorbent articles. Not only in fact the transverse cuts open the layered structure, therefore exposing the particulate material comprised therebetween, but the cutting action itself tends to break the particles with formation of powders and, which is more likely to occur in the layered absorbent structures described in the two above mentioned international applications, it can also break the bonding points created by the melted polymeric material between the particles and the fibrous layers. The problem of the loss of particulate material along the cut edges is therefore enhanced by these effects.
U.S. Pat. No. 4,715,918 by Kimberly-Clark Corporation and U.S Pat. No. 4,646,510 by Acumeter Lab. Inc., and European Patent EP-B-22792 by Beghin Say SA describe layered structures with particles embedded within two fibrous layers and confined in so called pockets or pouches which are created by the two fibrous layers joined by means e.g. of adhesive or fibre entanglement. The particles are to be selectively deposited on the substrate only on predetermined zones in order to form the pockets or pouches. These methods are capable of achieving a structure sealed both in longitudinal and in transverse direction, but are rather complex and are not suitable to produce pre-formed laminated structures that are to be subsequently fed to a production line and cut at predetermined intervals to form the individual layered absorbent structures.
It is therefore an object of the present invention to provide a process for manufacturing individual layered structures comprising a particulate material, which process prevents the loss or spillage of particulate material from the structures incorporating such material, particularly during the cutting step by which the individual layered structures are cut from a larger layered structure, e.g. a continuous, web-like layered structure.
It is a further object of the present invention to provide such a process that is applicable both to layered structures that are formed directly on the production line for the articles in which they are to be incorporated, and to continuous, web-like, layered structures that are produced as semi-finished intermediate products and are intended to be later fed to the production line.
It is still a further object of the present invention to provide individual layered structures that comprise a particulate material between containing layers that do not have the problem of loss or spillage of the particulate material from the edges thereof.